Rosai–Dorfman disease is a rare disorder caused by benign proliferation of histiocytes and thus also called sinus histiocytosis with massive lymphadenopathy [1]. It is typically known to involve lymph nodes but can also involve extra nodal sites in up to 23% patients, with breast involvement being extremely rare [2].
Most patients present as benign lump in breast, but many cases have been diagnosed in screening mammograms in asymptomatic women [2,3,4]. Radiological features are variable. It may present as a benign mass or fat necrosis and is known mimic malignancy on ultrasound and mammogram [2, 6]. Some cases may have skin thickening and synchronous or metachronous axillary lymphadenopathy [2].
The final diagnosis is through histopathological evaluation with the hallmark finding of emperipolesis along with S100 immunohistochemical staining that gives a definite diagnosis of Rosai–Dorfman disease. In addition, CD68 immunohistochemical staining confirms the inflammatory nature of the process involving macrophages and monocytes [6, 7]. In our case, the lesion had characteristic accumulation of histiocytes with few displaying emperipolesis with immunohistochemistry showing positivity for S-100 (Fig. 4e) and CD 68.
The disease usually spontaneously resolves and follows a benign course. In few cases, the disease may be progressive with solid organ involvement. These cases carry a bad prognosis especially with the involvement of kidney, liver and lower respiratory tract. In extremely rare cases, Rosai–Dorfman disease can be fatal [2, 8].
Till date no studies could be found to determine the best imaging modality to follow up Rosai–Dorfman disease outside breast. Some studies have shown 18F-fluorodeoxyglucose-positron emission tomography/CT for diagnosis, staging and follow-up [9, 10].
Considering the clinical presentation of a breast lump with skin discoloration and the imaging findings of a superficial, non-circumscribed, highly vascular lesion possibilities of low-grade primary angiosarcoma and hemangioma were considered among the differentials.
Primary angiosarcoma of breast is seen in young females typically in 3rd or 4th decade of life. It presents as a rapidly growing mass with bluish discoloration. Mammography shows non-circumscribed lesions which are heterogeneous on ultrasound with high vascularity on color Doppler. On MRI, they appear T2 hyperintense and T1 hypointense with high-intensity lakes of hemorrhage. Progressive enhancement is seen in low-grade tumors [11].
Breast hemangiomas are superficial subcutaneous or subdermal lesions which appear nonspecific circumscribed oval or lobular on mammography. On ultrasound, large lesions are heterogeneous and highly vascular with serpiginous vessels, often displaying a draining vessel. Limited literature on MRI appearance has shown benign morphological features with avid early enhancement [11, 12].